a) Field of the Invention
The present invention relates to a method for treating in a continuous manner an aqueous solution such as an industrial waste water, containing ions of a given type to be removed, especially heavy metal ions, in order to remove these ions from the solution.
b) Brief Description of the Prior Art
Numerous methods are already known and commonly used for treating ion-loaded aqueous solutions such as chromium plating solutions, mercury-polluted waters, contaminated brines and the like, in order to remove the polluting or deleterious ions contained in these solutions to make them usable, drinkable, reusable and/or recyclable.
These methods which are for the most part used in the industry for removing heavy metal ions such as mercury, cadmium, copper, zinc, nickel, cobalt or chromium in solution in waste waters, can be generally classified as follows:
1) methods in which the heavy metal ions are removed by ion exchange or adsorption (see U.S. Pat. Nos. 3,728,257; 4,167,481 and 4,481,087; see also Canadian patents Nos. 1,011,476 and 1,084,181); PA1 2) methods in which the aqueous solution to be treated is floculated with a suitable agent and allowed to settle, and PA1 3) methods in which the heavy metal ions are removed by direct precipitation with a salt dissolved in the solution (see U.S. Pat. Nos. 3,493,328; 3,552,917; 3,969,246; 4,054,517; 4,338,200; 4,401,573 and 4,465,598; see also Canadian patent No. 836,623). PA1 a) neutralizing the aqueous solution containing the ions to be removed if this solution is acidic; and PA1 b) passing the optionally neutralized solution through a container containing a metal salt that is sparingly soluble in water and thus will slightly dissolve in the aqueous solution to form a saturated solution of ions of the sparingly soluble salt that will permanently react with the ions to be removed to form therewith another salt which is insoluble in water and will precipiate, such a precipitation disturbing the equilibrium between the dissolved ions of the sparingly soluble salt and said sparingly soluble salt in undissolved form and thus causing more of said metal salt to dissolve and react with the ions to be removed. PA1 a container provided with an inlet and an outlet and containing a given amount of the metal salt which is sparingly soluble in water and has a greater affinity to react that the ions to be removed to form therewith the other salt which is insoluble in water; PA1 means such as a variable pump, for passing the aqueous solution to be treated through the container at such a speed as to allow the ions contained in the solution to contact the sparingly soluble salt and react therewith to form another insoluble salt; PA1 metering means for injecting a given amount of either an acid or a base into the aqueous solution to neutralize the same before it enters the container; and PA1 means such as a grid, at the outlet of the container for preventing the sparingly soluble and insoluble salts from being flushed out of this container when the aqueous solution is passing.